How is humidity typically expressed?

Relative humidity is typically used to express humidity because it provides a clear measure of the moisture content in the air relative to the maximum amount of moisture that the air can hold at a given temperature. It is expressed as a percentage and helps to indicate how close the air is to saturation. For example, a relative humidity of 50% means the air is holding half of the moisture it could potentially hold at that temperature.

Absolute humidity, while also a valid measure of humidity, quantifies the actual mass of water vapor present per unit volume of air, rather than providing a relative comparison to saturation levels. Specific humidity measures the mass of water vapor relative to the total mass of air, which includes both the water vapor and the dry air. Vapor pressure specifically looks at the pressure exerted by the water vapor in the air and does not express humidity in a straightforward percentage format.

By focusing on relative humidity, one can easily assess comfort levels and potential for condensation or evaporation, making it a practical and relevant measure in meteorology and fire investigation scenarios.